1. Field of the Invention
The present invention relates to a permanent magnet type generator to be mounted on a motor cycle, a beach buggy, a snowmobile or the like and, particularly, a generator that includes a rotor having 4n rare-earth permanent magnet poles and a stator having 3n teeth, wherein n is a positive integer.
2. Description of the Related Art
Recently a permanent magnet type generator is required to increase power in a lower speed range without increasing the axial size of the generator. However, it has been very difficult for a conventional permanent magnet type that includes a rotor having 2n rare-earth permanent magnet and a stator having 3n teeth.
JP-A-2003-348784 discloses a generator that includes a rotor having 4n rare-earth permanent magnet poles and a stator having 3n teeth around which stator coils are wound. The stator is comprised of a pair of thick core end plates and laminated thin core sheets sandwiched between the core end plates. Each core end plate has an upright flange portion at the periphery of the stator to face the inside surface of the rotor. Because the flange portion holds the stator coil and introduces effective magnetic flux of the permanent magnetic poles, the end core plate has a thickness sufficient to hold the coils and to introduce the magnetic flux.
Although the disclosed generator aims to meet the above stated requirement, the air gap between adjoining permanent magnet poles becomes so small that it suffers a considerable amount of eddy current loss on the core end plate because a ineffective portion or a leakage of the magnetic flux of the permanent magnet poles flows through the upright flange portions. Such an amount of the eddy current loss excessively heats the stator coils to damage the insulation coatings on the coils.
JP-A-2004-88955 discloses another generator that includes a rotor having 4n rare-earth permanent magnet poles and a stator having 3n teeth. However, the thick core end plates of the stator do not have upright flange portions. Therefore, it is difficult to hold the same size of the stator coils around the teeth. In other words, it is difficult to increase electric power in a lower speed range.